Apparatus for coating fibers

ABSTRACT

Apparatus for coating carbon, glass and like fibers to make a composite using resin, glass, metal etc., matrix comprises a plurality of rollers passing the fibers through a container of a slurry or solution of the matrix material. At least one fluid jet is provided urging the fibers away from contact with a roller. The fluid jet may be gas or the matrix material or both.

United States Patent Bowen et al.

' [451 Mar. 7, 1972 APPARATUS FOR COATING FIBERS Inventors: Dennis Herbert Bowen, North Stoke;

Neville John Mattiugley, Abingdon; Ronald Alired James Sambell, Reading, all of England Assignee: United Kingdom Atomic Energy Authority,

London, England Filed: Oct. 30, 1969 Appl No.: 872,593

Foreign Application Priority Data Nov. 1, 1968 Great Britain ..52,023/68 US. Cl. ..ll8/304, 28/75 R Int. Cl. ..D0ld 11/06 Field of Search ..1 18/74, 304, 206; 28/28, 72.6, 28/75 [56] References Cited UNITED STATES PATENTS 1,258,071 3/1918 Winter ..118/304 2,823,641 2/1958 Cook et al. ..1 18/74 Primary Examiner-Louis K. Rimrodt Attorney-Larson, Taylor and Hinds ABSTRACT Apparatus for coating carbon, glass and like fibers to make a composite using resin, glass, metal etc., matrix comprises a plurality of rollers passing the fibers through a container of a slurry or solution of the matrix material. At least one fluid jet is provided urging the fibers away from contact with a roller. The fluid jet may be gas or the matrix material or both.

5 Claims, 3 Drawing Figures APPARATUS FOR COATING FIBERS The present invention relates to apparatus for coating fibers. Such coated fibers are useable for forming a composite material, that is to say a material comprising a matrix reinforced with fibers. Such composite materials are well known and the fibers may for example be organic or inorganic fibers, glass and carbon fibers being the presently preferred material. Any suitable material may form the matrix.

It is the object of the present invention to provide a new or improved apparatus for coating fibers.

According to the present invention, there is provided apparatus for coating fibers comprising a plurality of rollers to receive a tow of fibers, a container for coating material, said rollers also serving to guide said tow into and through said container, at least one of the said rollers being a fiber input guide roller located for passage thereover of fibers prior to immersion in the coating material, the said fiber input guide roller having associated therewith a gas jet nozzle for directing a gas jet at the fibers at a location adjacent to the said fiber input guide roller, said gas jet serving to urge the fibers away from contact with the said fiber input guide roller.

In a preferred arrangement a plurality of jets are provided, each one originating from its associated nozzle. Thus prior to passing into the container the tow may pass under and over a plurality of rollers and at least one of said rollers has associated with it a gas jet, e.g., an airjet. Preferably two such gas jets are provided and are so orientated that there is no net endwise force exerted on the tow to urge it through the rollers.

In order to ensure adequate coating of the fibers by the coating material, they are preferably passed under. a roller which is at least partly submerged in the coating material in the container. A fluid jet of coating material may be directed at the upper side of the tow, adjacent to the said roller, to ensure even coating of the fibers. Alternatively a gas may be passed through the coating material in the container in order to stir the same to such an extent that an even coating of coating material is applied to the fibers.

After emerging from the said container, the tow preferably passes through at least one pair of biassed, e.g., spring-loaded rollers in order to compress it and remove excess coating material.

Very conveniently the tow is then passed to a takeup device and the separation between the container and the takeup device is such that partial, but not complete, drying of the coating material has taken place. In this way a sufficient thickness of impregnated tow is built up to enable a composite material to be made by further treatment. It is convenient to use a multisided drum as the takeup device and to use a roller to compress the tow lightly onto the drum, thereby to build up flat sheets ofprepreg material.

The fibers may be metal, carbon, glass or any suitable organic material, but this specification is chiefly concerned with carbon fibers.

The matrix material chosen will depend largely on the fibers but should be capable of being formed into a solution or suspension, with the aid of a binder if necessary. As possible matrix materials, we may mention glass, including nucleated glass, organic thermosetting and thermoplastic resins, metals, such as aluminum copper or silicon, oxides such as alumina or zirconia or cement, the latter in the form ofa self-curing aqueous slurry.

A specific construction of apparatus embodying the invention will now be described by way of example and with reference to the accompanying drawings, wherein:

FIG. 1 is a diagrammatic side view of the apparatus,

FIG. 2 is a side view ofa modified container, and

FIG. 3 is a side view ofa takeup device.

The apparatus of this example is for forming a continuous flat ribbon of carbon fibers coated with a material so that the coated fibers may be subsequently formed into a composite having, in this example, a glass matrix. Other composites may be formed, for example, by starting with powdered metal or other powdered material as above explained.

Referring to the drawing a tow 11 of continuous lengths of carbon fibers is drawn from a container 12. A suitable tow has, for example, 10,000 fibers each of nominal diameter 1.5 deni- The tow 11 passes over rollers 13,14 placed high and then under and over a series of rollers 15,16,17,18,19,21,41,42. Jet nozzles 25 and 26, connected to a source of compressed air, are arranged to direct a jet of air onto the tow ll of fibers as they pass over the rollers 16 and 21. The nozzles 25 and 26 have fishtail-shaped ends with the lengths of the elongated opening at the tail ends parallel with the axes of the rollers.

The nozzles 25 and 26 are arranged to direct the air jets so as to urge the fibers in the tow 11 away from the rollers 16 and 21 respectively.

As may be seen from-the drawing, the nozzle 25 is aligned so that the air is substantially tangential to the roller 16 at the point of contact of the tow 11 with the roller 16. Similarly the nozzle 26 is aligned so that the jet is substantially tangential to the roller 21 at the point where the tow 11 leaves contact with the roller 21. The driving effects of the air jets from the nozzles 25 and 26 upon the tow 11 are opposed so that there is no net tendency for the jets to drive the tow 11 one way or the other through the apparatus.

From roller 42 the tow 11 passes into slurry 27 in a tapered sided container 28 underneath a roller 22 which is partly submerged in the slurry 27. Coming out of the slurry, the tow 11 passes around rollers 23 and 24 which are lightly loaded, e.g., spring biased, towards one another to compact the coated fibers and control, to some extent, the pickup by squeezing off excess slurry.

The container 28 has sidewalls which taper to a l-inch diameter outlet at 44 from which slurry is pumped through a pipe (not shown) back into the top of the container. The purpose of the tapered sidewalls and vigorous recirculation of slurry from the bottom of the container is to avoid or reduce as far as possible separating out of the powdered glass.

Part of the recirculating slurry is pumped through a jet nozzle 31 which is fishtailed like the nozzles 25, 26 and arranged to supply a jet of slurry onto the tow 11 in such a direction as to urge the tow 11 away from the roller 22. This is effective to improve the uniformity of coating the two sides of the flat ribbon tow 11.

From roller 24, the tow 11 passes over a roller 43 which has a tapered sided groove for condensing the coated ribbon of fibers into a ribbon of the desired width, in this example onehalf inch width.

From roller 43, the tow 11 is conveyed horizontally over several feet to a rotating takeup device shown in FIG. 3 onto which the coated fibers are wound. The rotation of the device provides the drive which draws the tow 11 through the apparatus from the container 12.

In operation, the tow 11 is drawn at constant speed through the apparatus. The height of the rollers 13,14 encourages twists and kinks in the tow 11 to fall out before passage of the tow through the roller system, and in order to assist, the tow may pass through a set of curved spreader bars or banana bars prior to the roller 15.

The combined effect of the rollers l5,16,17,18,l9,21,41,42 and the air jets from the nozzles 25,26 is to fan out the fibers in the tow 11 into a flat ribbon. The width of the ribbon is defined by flanges on the rollers which follow the rollers at which the air jets are applied. In particular, the last roller 42 of the group of rollers is a flanged roller, the width between the flanges being equal to the desired output width of ribbon tow.

In a modified arrangement, as shown in FIG. 2, the container 28' is of rectangular form with a tapered base portion 50 below which is a porous glass filter plate 51 communicating with a plenum chamber 52 to which air is fed by pipe 53. The effect is to promote vigorous stirring in the container 28' and it is then not necessary to provide the pump recirculation and jet 31 of FIG. 1. The roller 22 of FIG. 1 is replaced by three rollers 54,55 and 56 which are well below the surface of the slurry 27. These three rollers, the roller 42 and the nip rollers 23,24 are all carried by side plates 57 so that all the rollers can be removed from the container 28' for cleaning.

The takeup device is shown in more detail in FIG. 3 and comprises a square-section drum 60 with side cheeks 61 mounted on an axle 62, the drum being rotated by a slipping drive 63 engaging one cheek 61. The tow 11 as it is laid up on the drum 60 is lightly pressed by a spring-loaded roller 64, to form sheets 65.

In this example the slurry comprises a mixture of 15 percent by volume powdered glass, 15 percent by volume polyvinylalcohol binder and 70 percent by volume methyl ethyl ketone solvent. The glass may, for example, be nucleated glass or borosilicate glass.

The composition of the slurry may be altered according to the speed with which the tow is to be driven, degree of pick up required and the desired composition of the ultimate composite. lt is believed that the proportions of the materials may be varied quite widely. For example 5 percent by volume glass, 5 percent by volume polyvinylalcohol and 90 percent by volume methyl ethyl ketone has been successfully employed experimentally.

For use with other fibers or other matrix materials, the composition of the slurry or solution may need to be determined by trial, having in mind the above factors.

As the coated tow 11 is drawn from roller 43 onto the drum 60, it undergoes partial drying. in this example, rectangular sheets of the composite material are to be formed, and the drum conveniently serves to form a preliminary laying up of the tow 11 which, on cutting at the corners of the drum, is ready for subsequent processing, which comprises subjecting the laid up fibers to heat and pressure.

This is conveniently carried out in a mold or die. For borosilicate glass the mold or die is conveniently formed of stainless steel and is coated with colloidal graphite as a parting agent. The treatment may comprise pressing at 5,000 p.s.i. at a temperature of 900 C. For nucleated glass a graphite mold or die is desirably employed, also coated with colloidal graphite as a parting agent. The treatment may comprise pressing at L500 p.s.i. at l,300C.

The surface properties of the composite may be modified by a coating applied to the composite during the pressing operation or subsequent thereto. This coating may for example be glass, a resin, or another inorganic refractory material such as silicon nitride. In the case of silicon nitride this is conveniently applied as a layer of silicon which is subsequently nitrided by known techniques. The application of a layer of glass, silicon, or indeed any other like powdered material is conveniently effected by coating both sides of the laid-up fibers, before the mold is closed with a layer of such powdered material dispersed in a binder. Very conveniently the technique used is to form a slurry of the powdered material in a suitable binder or binder mixture, desirably containing a solvent, and to deposit a layer of this slurry by means of a doctor blade or like technique upon a carrier. The layer is subsequently dried and may be partially cured to obtain a sufficiently flexible dry sheet which essentially comprises the powdered material in a binder. This dry sheet is then placed in contact with the laidup fibers and the pressing technique is such that it is caused to adhere to the surface of the final composite material.

The mold or die may, if desired, be lined with molybdenum foil or other refractory metal foil. This facilitates parting the mold and produces a gloss finish on the composite material.

The tow ll of carbon fibers which forms the starting material may be formed in accordance with the method described in British Pat. No. l l 1079].

The invention is not restricted to the details ofthc foregoing example. For instance, if the composite material is to have a ceramic or resin matrix, then the composition of the slurry and the subsequent treatment of the coated fibers is varied appropriately to the desired end product. The coated fibers need not necessarily be layed up with all the layers substantially parallel. For example alternate layers may be inclined to one another in a crisscross pattern.

Shapes other than rectangular sheets may be formed by appropriate shaping of the mold or die and appropriate laying up of the fibers.

We claim:

1. Apparatus for coating fibers comprising a plurality of rollers to receive a tow of fibers, a container for coating material, said rollers also serving to guide said tow into and through said container, at least one of the said rollers being a fiber input guide roller located for passage thereover of fibers prior to immersion in the coating material, the said fiber input guide roller having associated therewith a gas jet noule for directing a gas jet at the fibers at a location adjacent to the said fiber input guide roller, said gas jet serving to urge the fibers away from contact with the said fiber input guide roller to fan out the fibers in the tow into a flat ribbon prior to immersion of the tow into said coating material, and at least one further roller is located to be at least partly submerged in the said coating material in said container, the tow of fibers passing under such further roller, and a nozzle located above such further roller for directing onto the tow of fibers ajet of coating material, the axis of the nozzle being tangential to said further roller at the region of contact of the fibers with said further roller.

2. Apparatus as claimed in claim 1, including means for passing a gas through the coating material in said container to provide a stirring action.

3. Apparatus as claimed in claim 1, wherein at least one roller is located to be at least partly submerged in the said coating material, the tow of fibers passing under such roller, and a nozzle located above such roller for directing onto the tow of fibers a jet of coating material, the axis of the nozzle being tangential to the roller at the region of contact of the fibers with the roller.

4. Apparatus for coating fibers comprising a plurality of rollers to receive a tow of fibers, a container for coating material, said rollers also serving to guide said tow into and through said container, at least two of the said rollers being fiber input guide roller located for passage thereover of fiber prior to immersion in the coating material, the said fiber input guide rollers each having associated therewith a gas jet nozzle for directing a gas jet at the fibers at a location adjacent to the said fiber input guide roller, said gas jet serving to urge the fibers away from contact with the said fiber input guide roller to fan out the fibers in the tow into a flat ribbon prior to immersion of the tow into said coating material, said two gas jet nozzles being so orientated that, in operation, no net endwise force is exerted on the tow.

5. Apparatus as claimed in claim 4, wherein the axes of the gas jet nozzles are tangential to their associated rollers at the region of contact of the fibers with the roller. 

1. Apparatus for coating fibers comprising a plurality of rollers to receive a tow of fibers, a container for coating material, said rollers also serving to guide said tow into and through said container, at least one of the said rollers being a fiber input guide roller located for passage thereover of fibers prior to immersion in the coating material, the said fiber input guide roller having associated therewith a gas jet nozzle for directing a gas jet at the fibers at a location adjacent to the said fiber input guide roller, said gas jet serving to urge the fibers away from contact with the said fiber input guide roller to fan out the fibers in the tow into a flat ribbon prior to immersion of the tow into said coating material, and at least one further roller is located to be at least partly submerged in the said coating material in said container, the tow of fibers passing under such further roller, and a nozzle located above such further roller for directing onto the tow of fibers a jet of coating material, the axis of the nozzle being tangential to said further roller at the region of contact of the fibers with said further roller.
 2. Apparatus as claimed in claim 1, including means for passing a gas through the coating material in said container to provide a stirring action.
 3. Apparatus as claimed in claim 1, wherein at least one roller is located to be at least partly submerged in the said coating material, the tow of fibers passing under such roller, and a nozzle located above such roller for directing onto the tow of fibers a jet of coating material, the axis of the nozzle being tangential to the roller at the region of contact of the fibers with the roller.
 4. Apparatus for coating fibers comprising a plurality of rollers to receive a tow of fibers, a container for coating material, said rollers also serving to guide said tow into and through said container, at least two of the said rollers being fiber input guide roller located for passage thereover of fiber prior to immersion in the coating material, the said fiber input guide rollers each having associated therewith a gas jet nozzle for directing a gas jet at the fibers at a location adjacent to the said fiber input guide roller, said gas jet serving to urge the fibers away from contact with the said fiber input guide roller to fan out the fibers in the tow into a flat ribbon prior to immersion of the tow into said coating material, said two gas jet nozzles being so orientated that, in operation, no net endwise force is exerted on the tow.
 5. Apparatus as claimed in claim 4, wherein the axes of the gas jet nozzles are tangential to their associated rollers at the region of contact of the fibers with the roller. 